Serena Williams in 2012 won two Slams and the year-end Championships. She also regularly beat Victoria Azarenka and Maria Sharapova, the players ranked ahead of her. And yet — she wasn't No. 1.

Why?

One reason is that the WTA ranking system measures only which rounds a player reaches, not the players she beat to get there. Under the current rules, it doesn't matter whether you beat a tough player or a patsy; you get the same points.

Until 2006, there were points for beating top players as well as for reaching particular rounds. For instance, reaching the quarterfinal of an event by beating No. 1 and No. 8 was worth 143 points — 125 more points than you would get for beating No. 50 and No. 75.

These "quality points" were substantial — typically about a third of a player's total. And a larger margin of quality points was usually a good sign that a player had the potential to move up, while having less suggested a player was on the slide.

The table below (at the bottom of the story) shows the extra points players would have earned this season for beating top players (the quality points are divided by the number of tournaments played so players who play a lot and players who don't are measured on the same basis). These "quality rankings" reveal who's had the best wins this season, as opposed to the WTA rankings, which just look at the best results.

Naturally, Serena Williams not only comes out on top, she is on top by a wide margin.

Azarenka, meanwhile, is at No. 3 behind Sharapova, meaning that she did a good job of winning titles this year but not as well as the other two at beating other top players. Kim Clijsters didn't play a lot this farewell season, but her fourth position shows when she did, she was among the best

Williams addressed the discrepancy between the computer rankings and what many in the public believe is her place atop the sport during a recent exhibition tour in Africa with her older sister, Venus Williams.

"I'm not thinking about that (not being No. 1) so much," said Serena, who went 32-1 after losing in the first round of the French Open. "For me, I'd rather have Grand Slams and victories. I've been No. 1 before and believe me, I'll be No. 1 again. It's just a matter of time."

During a promotional shoot for one of her major sponsors on Friday in Los Angeles, Serena told USA TODAY Sports she stands by her comments.

"I say it because I believe it," said the 31-year-old American, who has not lost to Sharapova since 2004 and went 5-0 vs. Azarenka in 2012. "And I believe Victoria feels the same way. I believe Maria feels the same way. I even feel Agnieszka (Radwanska) feels that way. They all say it."

But she clarified that her public comments stemmed from a belief in her talent, not from any unfairness in the current ranking system.

"When I said that comment, I would say it again if I had to," she explained. "I wasn't saying it to say I deserved to be No. 1, because if I deserved to be No. 1 maybe I would have done better in Paris, maybe I would have done better in Australia. I would have been No. 1 without a doubt. I was just saying eventually I'll get there because I believe one day I'll get there. Because I believe in me. I believe with my talent I can be there. That's what that's more or less about."

The most significant mover might be Venus Williams, who stands dramatically higher in this ranking, at No. 8. That may be a little high, but she certainly looks bound for a comeback. Other players with a lot of "up side" include Kaia Kanepi, Yaroslava Shvedova, Svetlana Kuzetsova, Sabine Lisicki, Petra Martic, and Vera Zvonareva — all talented and dangerous players who have struggled with injury or inconsistency, but continue to post enough good wins to show they could recapture their previous form.

On the other hand, several players are revealing hidden weakness. Agnieszka Radwanska and Sara Errani come out lower than their rankings, showing that they've been relying on consistency more than knocking out the biggest names. Samantha Stosur and Marion Bartoli have dropped back this season, and the quality points show they're wilting against the top players. Maria Kirilenko's chances of going up further don't look that good. And Francesca Schiavone appears to be headed down further, since the quality of her wins are barely in the Top 50. But two of this season's biggest upward movers, Kerber and Vinci, show their progress has been on solid ground. And while Caroline Wozniacki has tumbled since the start of the season, at least it doesn't look like she's set to drop much further.

The figures also identify young players who are worth keeping an eye on, scoring wins above their rankings level. Kristina Pliskova is probably an outlier. But we'd look out for Camila Giorgi. Jamie Hampton, too, appears worthy of extra attention. But it's not clear Urszula Radwanska is that threatening yet. Madison Keys didn't quite make the Top 50 in this ranking, but her score is a lot higher than her WTA ranking; she looks like the best American hope at this time. Lauren Davis and Jana Cepelova also show signs of promise, although not quite as strong.

As for how much difference these points make, look no further than No. 1 — if quality points were included in the rankings, adjusting for other changes in the points table, Serena would be sitting on top there as well.